1. Field of the Invention
The present invention relates to a lighting circuit of an indicator lamp used for informing various states in a combination meter of a vehicle, etc.
2. Description of the Related Art
An indicator lamp informs various states in a combination meter of a vehicle. In this case, a switching transistor is provided on a feed circuit of the indicator lamp connected to a battery by switching on an ignition switch. The switching transistor is turned on/off by a control signal whose signal state changes according to a state to be informed.
It is to be noted that such an indicator lighting circuit also includes an indicator lighting circuit that pulls up a base potential of a switching transistor by power supply of the switching transistor to light an indicator lamp even in an open state of a signal line so as to be able to inform a state by the indicator lamp also at the time of disconnection of the signal line for the control signal (for example, Japanese Patent Application Laid-Open Publication No. 2002-29364).
Since the base potential of the switching transistor is pulled up by the power supply in the above-mentioned lighting circuit, the indicator lamp can inform the state only while an ignition switch is switched on, i.e., while the switching transistor is connected to the power supply.